Integrated circuit having a micromagnetic device including a ferromagnetic core and method of manufacture therefor

ABSTRACT

An integrated circuit and method of manufacturing therefor. In one embodiment, the integrated circuit includes a substrate with an insulator and a capacitor formed over the substrate. The integrated circuit further includes an adhesive formed over the insulator. The integrated circuit still further includes a micromagnetic device. The micromagnetic device includes a ferromagnetic core formed over the adhesive. The adhesive forms a bond between the insulator and the ferromagnetic core to secure the ferromagnetic core to the substrate. The micromagnetic device also includes at least one winding, located proximate the ferromagnetic core, to impart a desired magnetic property to the ferromagnetic core. The micromagnetic device is electrically coupled to the capacitor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to the following U.S. patent applications:

Reference No. Title Inventor(s) File Date Kossives 8-8-4- AMicromagnetic Kossives, June 10, 15-22 Device for Power et al. 1997Processing Applications and Method of Manufacture Therefor Kossives13-12- A Micromagnetic Kossives, July 2, 9-17-30 Device for Data et al.1998 Transmission Applications and Method of Manufacture ThereforKossives 14-15- A Micromagnetic Kossives, 11-19-32 Device having an etal. Anisotropic Ferromagnetic Core and Method of Manufacture therefor

The above-listed applications are commonly assigned with the presentinvention and are incorporated herein by reference as if reproducedherein in their entirety.

TECHNICAL FIELD OF THE INVENTION

The present invention is directed, in general, to integrated circuitsand, more specifically, to an integrated circuit having a capacitor anda ferromagnetic core and a method of manufacture therefor.

BACKGROUND OF THE INVENTION

A magnetic device includes a magnetic core coupled to conductor windingssuch that magnetic flux flows in a closed path about the core. Magneticdevices are generally configured in an EE-type structure or a toroidalgeometry. In the EE-type magnetic device, a first and secondcore-portion of the magnetic core surround the conductor windings. Inthe toroidal magnetic device, a first and second winding-portion of theconductor windings surround the magnetic core.

Micromagnetic devices (e.g., microinductors or microtransformers) aremicron-scaled integrated circuit magnetic devices; the electromagneticproperties of the device are provided by the presence of the magneticcore and conductor windings. In the past, micromagnetic devices wereonly applicable to low-level signal applications (e.g., recordingheads). With the advancement in production techniques for integratedcircuits, it is now possible to fabricate micromagnetic devices forrelatively large signal, power processing, high speed data transmissionand other applications. For instance, micromagnetic devices may beemployed in power systems for wireless communications equipment or indata transmission circuits.

While many power semiconductor devices (having ferrite cores, forinstance) have been scaled down into integrated circuits, inductiveelements at the present time remain discrete and physically large. Ofcourse, there is a strong desire to miniaturize these inductivecomponents as well. By extending thin-film processing techniquesemployed in power semiconductor devices to ferromagnetic materials, thesize of the conventional discrete ferromagnetic-core inductive devicescan be reduced significantly. Ferromagnetic materials such as alloys,however, have much higher saturation flux densities than ferrites (e.g.,10-20 kG verses 3 kG), thereby reducing the physical volume of the corefor a given inductance and energy requirement. To limit the eddy currentlosses in the ferromagnetic materials, the materials must be fabricatedin inordinately thin films. Processing thin-film ferromagnetic materialswith traditional rolling and tape winding techniques proves to be verycostly as the desired tape thicknesses drops below 0.001 inches (i.e.,25 μm). It is thus advantageous to produce such thin films by otherintegrated circuit deposition techniques such as sputtering orelectroplating.

Another germane consideration associated with manufacturingmicromagnetic devices is securing the ferromagnetic material to asilicon substrate or the like. More specifically, forming an adequatebond between the ferromagnetic material and an insulator coupled to thesubstrate is an important consideration. Many factors (such as oxideformation, melting point temperature, interposed contamination, affinitybetween materials and mechanical stress at the interface) may influencethe adhesion of a thin film to a substrate. For instance, one techniquereadily employed in thin film manufacturing processes is the formationof an oxide-metal bond at the interface between the substrate and thefilm. The oxide-metal bond may be formed by employing an oxygen-activemetal (such as tungsten or chromium) on an oxygen-bearing substrate(such as glass or ceramic) in conjunction with a refractory metal (suchas tantalum or tungsten). With regard to contaminants, it isadvantageous to remove any impurities interposed on the substrate.Cleaning methods vary in effectiveness and the method selected dependson the ability of the deposition process to dislodge contaminant atoms.As an example, different cleaning techniques may be employed withsputtering or electroplating.

Of course, the ultimate consideration with regard to the adhesionproperties depends on the materials employed. While others haveattempted to address the adhesion of ferromagnetic materials to aninsulator coupled to a substrate [e.g., Measured Performance of aHigh-Power-Density Microfabricated Transformer in a DC—DC Converter, byCharles R. Sullivan and Seth R. Sanders, IEEE Power ElectronicsSpecialists Conference, p. 287-294 (July 1996), which is incorporatedherein by reference] , to date, the problem remains unresolved. Thedevelopment of an adhesive material that simultaneously forms a bondwith the insulator and the ferromagnetic material such that thin-filmprocessing can be applied to inductive elements would provide afoundation for the introduction of micromagnetic devices into a varietyof integrated circuit applications.

Regarding magnetic properties, current micromagnetic devices aretypically isotropic in that their properties are the same when measuredin different directions. Although anisotropic properties are generallyknown in the domain of magnetics, anisotropic properties have not beenemployed in the design of micromagnetic devices due, in part, to thelimitations as addressed above regarding the fabrication ofmicromagnetic integrated circuits. Micromagnetic devices with theability to induce a designed magnetic anisotropic property into thecore, having a desired direction and characteristic, would be veryuseful.

Micromagnetic devices, which may be constructed using improved adhesivematerials and having a magnetic anisotropic property designed into thecore would facilitate a broad variety of integrated circuitapplications. Some of these micromagnetic application areas includecircuits for power processing, data transmission, radio frequency andmotor control integrated circuits. In summary, the ability to integratemicromagnetic devices with any other active or passive circuit componentsuch as transistors, diodes, capacitors, resistors and the like, to formessentially any totally integrated circuit would be very useful.

Accordingly, what is needed in the art is an integrated circuit that notonly includes a micromagnetic device, but includes other microcomponentssuch as capacitors and transistors.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, thepresent invention provides an integrated circuit and method ofmanufacturing therefor. In one embodiment, the integrated circuitincludes a substrate with an insulator and a capacitor formed over thesubstrate. The integrated circuit further includes an adhesive formedover the insulator. The integrated circuit still further includes amicromagnetic device. The micromagnetic device includes a ferromagneticcore formed over the adhesive. The adhesive forms a bond between theinsulator and the ferromagnetic core to secure the ferromagnetic core tothe substrate. The micromagnetic device also includes at least onewinding, located proximate the ferromagnetic core, to impart a desiredmagnetic property to the ferromagnetic core. The micromagnetic device iselectrically coupled to the capacitor. The integrated circuit may beemployed in various applications such as filter circuits.

In addition to the micromagnetic device, in a related, but alternativeembodiment, the integrated circuit includes a transistor formed on thesubstrate and electrically coupled to the ferromagnetic core. Thecapacitor, micromagnetic device and transistor may be employed withother components in RF circuits, power processing circuits or othercircuits.

The present invention introduces the broad concept of providing amicromagnetic device and capacitor in an integrated circuit. Thoseskilled in the art can readily understand the advantages and vastapplications for such devices in integrated circuits. The presentinvention in another aspect also introduces a transistor into theintegrated circuit thereby further expanding its applications. It shouldbe understood that other components may also be incorporated into theintegrated circuit and be within the broad scope of the presentinvention.

The foregoing has outlined, rather broadly, features of the presentinvention so that those skilled in the art may better understand thedetailed description of the invention that follows. Additional featuresof the invention will be described hereinafter that form the subject ofthe claims of the invention. Those skilled in the art should appreciatethat they can readily use the disclosed conception and specificembodiment as a basis for designing or modifying other structures forcarrying out the same purposes of the present invention. Those skilledin the art should also realize that such equivalent constructions do notdepart from the spirit and scope of the invention in its broadest form.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference isnow made to the following descriptions taken in conjunction with theaccompanying drawings, in which:

FIG. 1A illustrates a schematic diagram of an embodiment of a powerprocessing circuit constructed according to the principles of thepresent invention;

FIG. 1B illustrates a schematic diagram of an embodiment of a datatransmission circuit constructed according to the principles of thepresent invention;

FIG. 1C illustrates a schematic diagram of an embodiment of an RFcircuit constructed according to the principles of the presentinvention;

FIG. 1D illustrates a schematic diagram of a motor control circuitconstructed according to the principles of the present invention;

FIG. 2A illustrates a top view of an embodiment of a micromagneticdevice constructed according to the principles of the present invention;

FIG. 2B illustrates a top view of a micromagnetic device showing theresulting B-H curves for various external magnetic field orientations atdeposition;

FIG. 3 illustrates a top view of another embodiment of a micromagneticdevice constructed according to the principles of the present invention;

FIG. 4 illustrates a cross-sectional view of an embodiment of anintegrated circuit including a micromagnetic device constructedaccording to the principles of the present invention;

FIG. 5A illustrates a schematic diagram of an embodiment of a low passfilter circuit constructed according to the principles of the presentinvention;

FIG. 5B illustrates a cross-sectional view of an integrated circuitshowing an embodiment of the low pass filter circuit of FIG. 5Aconstructed according to the principles of the present invention;

FIG. 5C illustrates a top view of the integrated circuit shown in thecross-section of FIG. 5B, which represents an embodiment of the low passfilter circuit of FIG. 5A;

FIG. 6A illustrates a schematic diagram of a high pass filter circuitconstructed according to the principles of the present invention;

FIG. 6B illustrates a cross-sectional view of an integrated circuitshowing an embodiment of the high pass filter circuit of FIG. 6Aconstructed according to the principles of the present invention;

FIG. 7A illustrates a schematic diagram of a bandpass filter constructedaccording to the principles of the present invention;

FIG. 7B illustrates a schematic diagram of a notch filter constructedaccording to the principles of the present invention; and

FIG. 8 illustrates a flow diagram of an embodiment of a method ofmanufacturing the integrated circuit of FIG. 6B.

DETAILED DESCRIPTION

Referring initially to FIG. 1A, illustrated is a schematic diagram of anembodiment of a power processing circuit 10 constructed according to theprinciples of the present invention. The power processing circuit 10includes a power train having a conversion stage including a switchingcircuit 15 for receiving input electrical power V_(IN) and producingtherefrom switched electrical power. The power processing circuit 10further includes a filter circuit (including an output inductor 43 andoutput capacitor 48) for filtering the switched electrical power toproduce output electrical power (represented as a voltage V_(OUT)).

The power processing circuit 10 still further includes a powermicromagnetic device (e.g., transformer) 20, having a primary winding 23and a secondary winding 26, and a rectifier (including rectifying diodes30, 40) coupled between the power conversion stage and the filter stage.In accordance with the principles as hereinafter described, the powerprocessing circuit 10 including, for instance, the transformer 20, theoutput inductor 43 and the output capacitor 48, may be formed into anintegrated circuit. It should be clear, however, that the powerprocessing circuit 10 is submitted for illustrative purposes only andother circuits and applications therefor are well within the broad scopeof the present invention.

Turning now to FIG. 1B, illustrated is a schematic diagram of anembodiment of a data transmission circuit 50 constructed according tothe principles of the present invention. The data transmission circuit50 includes a first communications circuit 55 for receiving acommunications signal. The data transmission circuit 50 further includesa second communications circuit 75 for transmitting the communicationssignal. The data transmission circuit 50 further includes a transmissionline cable 65 having a characteristic impedance Z_(o), coupling thefirst communications circuit 55 to the second communications circuit 75.The data transmission circuit 50 still further includes first and seconddata transmission micromagnetic devices 60, 70, coupled between thetransmission line cable 65 and the first and second communicationscircuits 55, 75, respectively. The first and second data transmissionmicromagnetic devices 60, 70 are constructed according to the principlesof the present invention as hereinafter described.

In the illustrated embodiment, the first and second data transmissionmicromagnetic devices 60, 70 may perform several functions including,without limitation, voltage transformation, impedance transformationfrom a transmitter impedance of the second communications circuit 75 tothe characteristic impedance Z_(o) and from the characteristic impedanceZ_(o) to a receiver impedance of the first communications circuit 55.Other functions include unbalanced to balanced signal conversion andelectromagnetic interference suppression. In accordance with theprinciples as hereinafter described, the data transmission circuit 50including, for instance, first and second data transmissionmicromagnetic devices 60, 70, may be formed into an integrated circuit.The data transmission circuit 50 and first and second data transmissionmicromagnetic devices 60, 70 are submitted for illustrative purposesonly and other circuits and applications therefor are well within thebroad scope of the present invention.

Turning now to FIG. 1C, illustrated is a schematic diagram of anembodiment of an RF circuit 100 constructed according to the principlesof the present invention. The RF circuit 100 includes an N-channelMOSFET 110, a micromagnetic inductor 120 and a capacitor 130. The RFcircuit 100 is an RF amplifier that receives an input signal Vin at anRF frequency determined by the resonant frequency of the parallelcombination of the micromagnetic inductor 120 and the capacitor 130. Anamplified output signal Vout may then be provided to another circuit asappropriate. The n-channel MOSFET 110, the micromagnetic inductor 120and the capacitor 130 are constructed according to the principles of thepresent invention as hereinafter described. Of course, the RF circuit100 is exemplary of other RF circuits such as filters, modulators,demodulators or other parallel or series tuned circuits that may beemployed.

Turning now to FIG. 1D, illustrated is a schematic diagram of a motorcontrol circuit 150 constructed according to the principles of thepresent invention. The motor control circuit 150 includes a rectifiersystem 155, a micromagnetic inductor 160, a capacitor 165, aninverter/controller system 170 and a motor 175. The rectifier system155, which may accommodate single-phase or three-phase AC supplies,converts an AC voltage to a DC voltage, and the combination of themicromagnetic inductor 160 with the capacitor 165 forms a low passfilter to further smooth the DC voltage presented to theinverter/controller 170. The inverter/controller 170 then converts theDC voltage into a three-phase signal that drives the motor 175. Theinverter/controller 170 may use a pulse width modulation (PWM) techniqueto allow variable motor speed control. The motor control circuit 150including, for instance, the low pass filter (the micromagnetic inductor160 and the capacitor 165) as well as the rectifier system 155 and theinverter/controller system 170 are constructed according to theprinciples of the present invention as hereinafter described.

Turning now to FIG. 2A, illustrated is a top view of an embodiment of amicromagnetic device 200 constructed according to the principles of thepresent invention. The micromagnetic device 200 is an EE-typetransformer device. The micromagnetic device 200 includes aferromagnetic core having a first core-portion 210 and a secondcore-portion 215. While the ferromagnetic core may be composed of analloy (e.g., a permalloy™ composed of nickel-iron including about 80%nickel and 20% iron), other ferromagnetic materials are well within thebroad scope of the present invention. The micromagnetic device 200 alsoincludes conductive windings having a primary winding 220 and asecondary winding 225. Of course, the windings may be formed from anyconductive material. The primary winding 220 terminates in a pluralityof terminals 230, 235; the secondary winding 225 terminates in aplurality of terminals 240, 245.

The first and second core-portions 210, 215 surround the primary andsecondary windings 220, 225. The magnetic flux of the micromagneticdevice 200 predominantly flows along the width of the ferromagneticcore. As a result, the ferromagnetic core is anisotropic, therebycontrolling hysteresis losses at higher frequencies (e.g., above 10MHZ). The first and second core-portions 210, 215 may be coupledtogether by magnetic vias (when anisotropic characteristics and controlare desired) or remain separate (when an air gap is desired). TheEE-type structure effectively controls the permeability of theferromagnetic core by regulating the direction of the induced anisotropywith respect to the magnetic field vector.

With regard to the ferromagnetic material, the total thickness thereofis selected based on the inductance requirements of the device. Foroperation at relatively high frequencies (e.g., above 10 MHZ), eddycurrents induced in the ferromagnetic materials can become problematicdue to the resulting low resistivity (e.g., ρ˜20-100 μΩcm). To reducethe eddy currents, the magnetic film thickness of the ferromagneticmaterial should be limited to a fraction of the skin depth δ [whereδ=(ρ/nfμ)^(½) for a given frequency f of operation]. For instance, at 8MHZ and μ=1000, the skin depth is about 2.5 μm; thus, to limit theeffect of the eddy currents, the film thickness should be below about 2μm (obviously, thinner films are necessary as the permeabilityincreases). When the inductance specification requires a largerthickness, insulated multiple layers of film (with each layer notexceeding the necessary skin thickness) should be employed.

For use in data transmission applications, for instance, performance ofthe micromagnetic device 200 at high data transmission rates may beaffected by parasitic elements. Leakage inductances and interwindingcapacitances may cause distortions, overshoots, and backswings that mayplace a transmitted pulse of data outside an acceptable transmissiontemplate. Such parasitic elements may be influenced by a physical sizeand arrangement of the micromagnetic device 200. The parasitic elements,however, may be reduced by miniaturizing the micromagnetic device 200using the principles of the present invention.

Turning now to FIG. 2B, illustrated is a top view of a micromagneticdevice 250 showing the resulting B-H curves for various externalmagnetic field orientations at deposition. The B-H curve is a plot ofmagnetic flux density (B) verses magnetic magnetizing force (H) for amagnetic material. As discussed in FIG. 2A, the magnetic flux of themicromagnetic device 200 predominantly flows along the width of theferromagnetic core. This effect causes the ferromagnetic core to beanisotropic due to the construction geometry. An anisotropy property mayalso be introduced during the deposition process, when conducted in anexternal magnetic field, using an energized solenoid or permanentmagnet. The external magnetic field is normally uniform and may beapplied at levels of 10-500 Oersteds [(“Oe”); 8000-40000 A/m]. Ofcourse, some cases may exist where the application of a non-uniformexternal magnetic field may be useful. In the present embodiment, theinduced anisotropy produces both a hard axis and an easy axis, alongwhich the permeability is a minimum and maximum, respectively.Additionally, the hard axis and the easy axis are seen to besubstantially transverse in this embodiment. Of course, otherembodiments may employ other orientations between the hard axis and theeasy axis.

The micromagnetic device 250 shows a hard axis B-H curve 260 and an easyaxis B-H curve 270. Permeability is proportional to the slope of the B-Hcurve, typically defined in the middle region of the B-H curve, whichcorresponds to the non-saturated operating region of the magnetic core.In some cases, the permeability may be increased five-fold from the hardaxis to the easy axis as a result of the anisotropy. An intermediateaxis B-H curve 280 is also shown, which has characteristics differentfrom the hard axis and easy axis B-H curves 260, 270. The intermediateB-H curve 280 is typical of tailored B-H curves, which may be createdduring deposition of the micromagnetic core by orienting the externalmagnetic field in a desired direction.

Turning now to FIG. 3, illustrated is a top view of another embodimentof a micromagnetic device 300 constructed according to the principles ofthe present invention. The micromagnetic device 300 is a toroidaltransformer device. The micromagnetic device 300 includes aferromagnetic core 310 (proximate a window 325) and conductive windings(collectively designated 350) that surround the ferromagnetic core 310through inner-layer connection vias (one of which as designated 375) andterminate in a plurality of terminals 380, 385, 390, 395. Theinner-layer connection vias 375 lie within the window 325.

Rules regarding line space and via-to-via distance determine the size ofthe window 325. Obviously, with the trend towards smaller devices, asmaller window dimension is desirable. The dimension of the window 325,however, is limited by the thickness of the ferromagnetic materialnecessary to achieve the required inductance characteristics. Forexample, the inductance of a toroidal device is maximized if the toroidis generally circular. The inductance is less if the toroid is formedinto a square (˜25% less), degrading further as the square is elongatedinto a rectangle. The inductance L for a square toroid having a corewidth to meet a minimum window dimension, is:

L=μ ₀ [N ² t]/4(1+Π)

where N is the number of turns of the conductive windings 350 and t isthe thickness of the film. The size of the window 325 is determined bythe minimum via size, via—via clearance and the number of vias (relatedto the number of primary and secondary turns). Therefore, to reduce thedie size of the device, a larger core thickness is necessary to obtainan equivalent inductance to an EE ferromagnetic core of equal windingturns and core width.

Remember that, for the EE-type structure, fewer winding connection viasare required, thereby reducing the amount of die space necessary tocouple the windings to the core. Toroidal transformers, however, offer arelatively flat and smooth surface for the deposition of theferromagnetic material, thereby reducing the formation of stresses thatmay degrade the magnetic properties of the film deposited thereon. Thisis especially important when the ferromagnetic material has a highmagnetostriction constant. The EE-type structure also requires specialprovisions to create a continuous magnetic path from the firstcore-portion to the second core-portion. This is accomplished byintroducing vias within the central core region and at the two outercore edges. The vias provide connectivity for the ferromagnetic materialsuch that the first and second core-portions are coupled togethercontinuously. The vias, however, are a source of stress concentrationthat require additional slope reduction to decrease the accumulatedstresses.

While FIGS. 2 and 3 illustrate both the EE-type and toroidal transformerdevice (including the advantages and disadvantages thereof), othermicromagnetic devices (including variations of the foregoing devices)and applications therefor are well within the broad scope of the presentinvention.

Turning now to FIG. 4, illustrated is a cross-sectional view of anembodiment of an integrated circuit 400 including a micromagnetic deviceconstructed according to the principles of the present invention. Theintegrated circuit 400 may be employed in a power processing, datatransmission or any other circuit. The integrated circuit 400 includes asubstrate (composed of, for instance, silicon, glass, ceramic or thelike) 410 having a passivation layer (e.g., silicon-dioxide) 420 formedthereon using conventional formation processes such as a thermal growingprocess. The integrated circuit 400 further includes first and secondconductive winding layers (composed of, for instance, aluminum or anyother conductive material) 440, 460 surrounded by first, second andthird insulative layers or insulators 430, 450, 470. The integratedcircuit 400 still further includes an adhesive (a metallic adhesive inthe illustrated embodiment) that contains a first adhesive layer (e.g.,chromium) 480 and a second adhesive layer (e.g., silver) 485. Theintegrated circuit 400 still further includes a ferromagnetic core 490.The integrated circuit 400 still further includes a plurality ofinner-layer vias (collectively designated 493) that provide multiplepaths between layers of the integrated circuit 400 and a terminal 496for connection to another device.

The passivation layer 420 and first, second and third insulative layers430, 450, 470 may be formed from an inorganic composition (e.g.,silicon-dioxide, aluminum-dioxide, beryllium-dioxide), an organicpolymer (e.g., a polyimide) or any other insulating material. Themetallic adhesive is an inorganic-based material that is substantially(about 70%) free of titanium. While the first adhesive layer 480generally contains materials selected from Group 4 elements (such aszirconium and hafnium; excluding about a 70% or more composition oftitanium), Group 5 elements (such as vanadium, niobium and tantalum) andGroup 6 elements (such as chromium, molybdenum and tungsten), otherelements are well within the broad scope of the present invention. Itshould be noted that the above classifications of elements arecompatible with the new International Union of Pure and AppliedChemistry notation indicated in the periodic table. Additionally, whilethe second adhesive layer 485 generally contains metals such as gold,silver, platinum, palladium and copper, other materials susceptible toplating a ferromagnetic material are well within the broad scope of thepresent invention. Again, while the ferromagnetic core 490 may becomposed of an alloy (such as a permalloy™ or a cobalt-ironcomposition), other ferromagnetic materials (e.g., an amorphous nickelphosphide) are well within the broad scope of the present invention.

As previously mentioned, it is desirable to manufacture micromagneticdevices as integrated circuits. Employing alloys in the ferromagneticcore 490 is attractive since the relatively low magnetostrictionconstants may reduce the stress associated with the depositionprocesses. If relatively high stresses are associated with thedeposition process, the magnetic properties of the integrated circuit400 may be degraded and the thin films may lack the requisite adhesiveproperties necessary to facilitate the deposition of the integratedcircuit 400. Obviously, an adhesive that counteracts the potentialbuilt-up stress in the films should be provided.

Several attempts have been undertaken to uncover an adhesive thatprovides a secure interface to a ferromagnetic material and aninsulator. For instance, when a metal such as silver is exclusively usedas the adhesive, the ferromagnetic material/silver interface is strongerthan the insulator/silver interface. As a result, the ferromagneticmaterial and silver films may be peeled away from the substrate at aspecified testing peel force (using a standard adhesion evaluationtechnique for less than 1 kG/cm²). Conversely, when chromium isexclusively used as the adhesive, the insulator/chromium interface isstronger than the ferromagnetic material/chromium interface. As aresult, the ferromagnetic material and silver films may be peeled awayfrom the substrate at a specified testing peel force (using a standardadhesion evaluation technique for less than 1 kG/cm2). Additionally, thechromium does not provide an adequate seed layer for plating theferromagnetic material. In conjunction with present invention,therefore, an adhesive is disclosed (as described above) that providesan adequate bond between the ferromagnetic core 490 and the insulators430, 450, 470 coupled to the substrate 410 to facilitate the fabricationof the integrated circuit 400.

Turning now to FIG. 5A, illustrated is a schematic diagram of anembodiment of a low pass filter circuit 500 constructed according to theprinciples of the present invention. The low pass filter circuit 500includes first and second micromagnetic inductors 511, 512 and acapacitor 513 as shown. An input voltage Vin may be applied betweenterminals 501, 503, and a resulting output voltage Vout may be observedbetween terminals 502, 503. It is well understood that the magnitude ofthe output voltage Vout is frequency dependent and diminishes withincreasing frequency beyond a cutoff frequency determined by the valuesof the first and second micromagnetic inductors 511, 512 and thecapacitor 513.

Turning now to FIG. 5B, illustrated is a cross-sectional view of anintegrated circuit 525 showing an embodiment of the low pass filtercircuit of FIG. 5A constructed according to the principles of thepresent invention. The integrated circuit 525 includes a substrate 538,first, second, third and fourth insulators 539, 540, 541, 542 formedover the substrate 538, a capacitor 513 and first and secondmicromagnetic devices 511, 512 formed over the substrate 538. Thecapacitor 513 includes first and second capacitor plates 532, 533 and adielectric layer 534. The first and second micromagnetic devices 511,512 include an adhesive, which may be a metal adhesive comprising aplurality of layers, formed over the second insulator 540 that forms abond between the second insulator 540 and first and second ferromagneticcores 529, 535 according to the principles detailed previously in FIG.4. The first and second ferromagnetic cores 529, 535 may contain analloy material, and the second, third and fourth insulators 540, 541,542 may be an organic polymer. The first insulator 539 is typicallysilicon dioxide, and the dielectric 534 is typically silicon nitride. Ofcourse, other core, insulator and dielectric materials may be used asappropriate.

The first and second micromagnetic devices 511, 512, which areelectrically coupled to the capacitor 513, further include first andsecond windings 530, 536, respectively, located proximate the first andsecond ferromagnetic cores 529, 535 to impart a desired magneticproperty thereto. The integrated circuit 525 further includes first,second and third terminals 501, 502, 503 connected to the first andsecond micromagnetic devices 511, 512 and the capacitor 513,respectively. The first and second micromagnetic devices 511, 512 andthe capacitor 513 are interconnected to form the low pass filter circuit500 illustrated in FIG. 5A.

Turning now to FIG. 5C, illustrated is a top view of the integratedcircuit 525 that is shown in the cross-section of FIG. 5B representingan embodiment of the low pass filter circuit 500. The top view of theintegrated circuit 525 shows the first and second micromagnetic devices511, 512 and the capacitor 513. Details of the first and second windings530, 536 are more clearly seen as are the interconnects between thefirst and second micromagnetic devices 511, 512 and the capacitor 513.

Turning now to FIG. 6A, illustrated is a schematic diagram of a highpass filter circuit 600 constructed according to the principles of thepresent invention. The high pass filter circuit 600 includes atransistor (e.g., a MOSFET) 610, a capacitor 611, a micromagneticinductor 612 and first, second, third and fourth terminals 601, 602,603, 604. An input voltage Vin may be applied between the first andsecond terminals 601, 602 and an amplified, frequency-sensitive outputvoltage Vout may be obtained between the first and fourth terminals 601,604. The first and third terminals 601, 603 are used for connecting abias supply voltage to the MOSFET 610. For a constant amplitude inputvoltage Vin, the output voltage Vout increases directly with frequencyuntil a frequency is reached where the output voltage Vout essentiallybecomes constant with frequency. This point is determined by the valuesof the capacitor 611 and the micromagnetic inductor 612.

Turning now to FIG. 6B, illustrated is a cross-sectional view of anintegrated circuit 625 showing an embodiment of the high pass filtercircuit 600 of FIG. 6A constructed according to the principles of thepresent invention. The integrated circuit 625 includes a substrate 638,first, second, third and fourth insulators 639, 640, 641, 642 formedover the substrate 638, a MOSFET 610, a capacitor 611 and amicromagnetic inductor 612 also formed over the substrate 638. TheMOSFET 610 includes a source area 629, a drain area 630 and a gate area631. The capacitor 611 includes first and second capacitor plates 632,633 and a dielectric layer 634. The micromagnetic inductor 612 includesan adhesive, which may be a metal adhesive comprising a plurality oflayers, formed over the second insulator 640 that forms a bond betweenthe second insulator 640 and a ferromagnetic core 635 according to theprinciples detailed previously in FIG. 4. The ferromagnetic core 635 maycontain an alloy material, and the second, third and fourth insulators640, 641, 642 may be an organic polymer. The first insulator 639 istypically silicon dioxide, and the dielectric 634 is typically siliconnitride. Of course, other core, insulator and dielectric materials maybe used as appropriate.

The micromagnetic inductor 612, which is electrically coupled to theMOSFET 610 and the capacitor 611, further includes a winding 636 locatedproximate the ferromagnetic core 635 to impart a desired magneticproperty. The integrated circuit 625 further includes first, second,third and fourth terminals 601, 602, 603, 604 connected to the MOSFET610, the capacitor 611 and the micromagnetic inductor 612 as shown TheMOSFET 610, the capacitor 611 and the micromagnetic inductor 612 areinterconnected to form the high pass filter circuit 600 illustrated inFIG. 6A.

Turning now to FIG. 7A, illustrated is a schematic diagram of a bandpassfilter circuit 700 constructed according to the principles of thepresent invention. In this embodiment, the bandpass filter circuit 700includes a micromagnetic inductor 705 and a capacitor 710 connected in aparallel arrangement as shown. An output voltage Vout is a frequencydependent function of an input voltage Vin. For a constant amplitudeinput voltage Vin, the output voltage Vout peaks in amplitude at afrequency determined by the values of the micromagnetic inductor 705 andthe capacitor 710. Other embodiments may include a transistor or othercircuit elements. This embodiment and other embodiments may beconstructed in a manner similar to the integrated circuit 525 of FIG. 5Bor the integrated circuit 626 of FIG. 6B as described above.

Turning now to FIG. 7B, illustrated is a schematic diagram of a notchfilter circuit 750 constructed according to the principles of thepresent invention. The notch filter circuit 750 includes first andsecond capacitors 760, 780 and a micromagnetic inductor 770. An outputvoltage Vout is also a frequency dependent function of an input voltageVin. For a constant amplitude input voltage Vin, the output voltage Voutdrops to a minimum value at a frequency determined by the values of thefirst and second capacitors 760, 780 and the micromagnetic inductor 770.Other embodiments may include a transistor or other circuit elements.This embodiment and other embodiments may be constructed in a mannersimilar to the integrated circuit 525 of FIG. 5B or the integratedcircuit 625 of FIG. 6B as described above.

Turning now to FIG. 8, illustrated is a flow diagram of an embodiment ofa method (generally designated 800) of manufacturing the integratedcircuit 625 of FIG. 6B. Portions of the method of manufacturing theintegrated circuit 625 are analogous to conventional silicon-on-siliconmulti-chip-module processes [see Silicon-on-Silicon MCMs with IntegratedPassive Components, by R. C. Frye, et al., Proc. 1992 IEEE Multi-ChipModule Conference, p. 155, Santa Cruz, Calif. (March 1992), which isherein incorporated by reference] with the following variations.Generally, a photolithographic process with photoresist is used todefine the geometrical features of the integrated circuit based upon a10-20 μm design rule. While the rule is relatively coarse, it isadequate for fabricating devices such as the integrated circuit 625since the major dimensions are multiples of the 10-20 μm rule. Thephotolithographic process generally includes the steps of exposing anddeveloping the photoresist. The photolithographic process also includesetching and stripping away unwanted portions of the material to whichthe process is being applied. Those skilled in the art should befamiliar with conventional photolithographic processes.

The method begins at a start step 801 with a silicon substrate. Sourceand drain areas for the MOSFET 610 are diffused into the siliconsubstrate in a diffuse source and drain step 805. These diffusion areasare n-type diffusions requiring a p-substrate for the MOSFET polarityshown in FIG. 6A. Of course, the polarities may be reversed if anopposite polarity MOSFET is desired. Then, contacts for the source anddrain are formed in a form contacts step 810. The silicon substrate isoxidized with a passivation layer in an oxidize substrate step 820. Thepassivation layer is generally created using conventional thermalgrowing techniques or chemical vapor deposition techniques. Of course,the substrate may be blank or may be composed of a pre-fabricated waferwith underlying circuitry and final passivation.

Next, a gate is deposited for the MOSFET in a deposit gate step 822, andthen a first capacitor plate is deposited for the capacitor in a depositfirst capacitor plate step 824. The integrated circuit 625 employs atoroidal micromagnetic device structure that includes multiple layers. Afirst conductive winding layer is then blanket deposited on thesubstrate during a deposit first conductive winding layer step 830. Thefirst conductive winding layer may be composed of aluminum, having athicknesses of about 2-10 μm, that is sputter deposited (for instance,at 5 mtorr Argon pressure and room temperature) on the passivationlayer. For thicker conductor traces (to achieve lower resistance),electroplated copper may be used, resulting in thicknesses up to about25 μm.

A contact for the gate is then formed in a form gate contact step 823,and a contact for the first capacitor plate is formed in a form contactto first capacitor plate step 825. The first conductive winding layer isthen patterned to the desired configuration (including the desiredcontact regions for the integrated circuit) using a conventionalphotolithographic process in a form contacts for first conductivewinding layer step 835. Of course, another contact region may be formedin the first conductive winding layer to facilitate electricalconnectivity to other circuits coupled to the substrate as required.

A dielectric layer for the capacitor is then deposited in a depositdielectric layer step 826. The dielectric layer is typically composed ofsilicon nitride, but other materials may be used as appropriate. Thefirst insulative layer may then be spin coated on the passivation layer,existing MOSFET and capacitor structures and the first conductivewinding layer during a deposit first insulative layer step 840. Thefirst insulative layer is then cured (at about 350° C. for approximately12 hours). After shrinkage, the insulative layer is about 3-5 μm thick.The spin coating techniques generally provide higher voltage isolationbetween primary and secondary micromagnetic device windings. The voltagelevel breakdown values for isolation vary from 500 volts alternatingcurrent (“VAC”) to 3000 VAC. The first insulative layer is thenpatterned using a conventional photolithographic process to forminner-layer vias therethrough.

A second capacitor plate is then deposited in a deposit second capacitorplate step 842, and the metallic adhesive, including the first andsecond adhesive layers, is blanket deposited on the first insulativelayer during an apply metallic adhesive layer step 850. The firstadhesive layer may be composed of chromium, sputter deposited (forinstance, at 5 mtorr Argon pressure and 250° C.) to a thickness of about250 Å on the first insulative layer. The second adhesive layer may becomposed of silver, sputter deposited (for instance, at 5 mtorr Argonpressure and room temperature) to a thickness of about 500 Å on thefirst adhesive layer. The metallic adhesive also serves as a seed layerfor plating the ferromagnetic core.

A contact is formed to the second capacitor plate in a form contact tosecond capacitor plate step 844, and the ferromagnetic core is deposited(e.g., electroplated to a thickness of about 2-12 μm) on the metallicadhesive during a deposit ferromagnetic core step 860. The ferromagneticcore may be plated in a buffered sulfamate bath under a controlledtemperature (e.g., 25-35°° C.) with a current density of about 30mA/cm². The metallic adhesive and ferromagnetic core are patterned tothe desired configuration using a photolithographic process.

With regard to the photolithographic process, the etching solutionsshould be capable of removing the unwanted metallic adhesive (e.g.,chromium-silver composition) without attacking the depositedferromagnetic film. For instance, a standard commercial cerric ammoniumnitrate (“CAN”) formulation etch solution etches the silver at the rateof about 50 Å/sec and etches the chromium at the rate of 250 Å/minwithout substantially affecting the ferromagnetic material. Thus,employing a CAN etch for approximately 60-75 seconds is adequate topattern the metallic adhesive and ferromagnetic core. Again, the firstadhesive layer (e.g., chromium) is preferably deposited in the range of200-300 (250 nominal) Å and the second adhesive layer (e.g., silver) ispreferably deposited in the range of 400-600 (500 nominal) Å tofacilitate a controllable etch process.

Furthermore, to eliminate possible lateral etching and undercuttingbeneath the ferromagnetic core, the second adhesive layer may becomposed of copper. In this case, a potassium iodide and water solutionmay be applied for about 10 seconds to perform the copper etchingprocess and a potassium ferri-cyanide and potassium hydroxide solutionmay be applied for about 1-2 seconds to perform the chromium etchingprocess. The potassium ferri-cyanide and potassium hydroxide solutiondoes not substantially affect the copper layer underlying theferromagnetic core, thereby preventing the potential affects ofundercutting. Of course, other types of etching processes (such as ionetching) are well within the broad scope of the present invention.Additionally, an external magnetic field, as described in FIG. 2B, maybe applied during the deposit ferromagnetic core step 860 to achieve atailored B-H curve and, for instance, a specific permeability.

The second insulative layer is spin coated on the ferromagnetic core andthe first insulative layer during a deposit second insulative layer step870. The second insulative layer is then patterned using aphotolithographic process to form the inner-layer vias therethrough. Thesecond conductive winding layer is then blanket deposited (e.g.,sputtered) on the second insulative layer during a deposit secondwinding conductive layer step 880. The second conductive winding layeris then patterned to the desired configuration (including the desiredcontact regions) using a photolithographic process. Next, the thirdinsulative layer is spin coated on the second conductive winding layerand the second insulative layer during a deposit third insulative layerstep 890. Terminals are finally formed in the third insulative layerduring a form terminal step 895. The terminals are either suitable forwire bonding (e.g., aluminum wire bonding) or may be finished with asolder-wettable metal (e.g., chromium) for use with solder pastes forflip-chip assembly as shown in FIG. 6E. The method terminates at an endstep 899. A completed wafer may then be packaged as an integratedcircuit or bare die mounted as in flip-chip assemblies.

While the preceding FIGURES illustrate embodiments of an integratedcircuit for use in power processing, data transmission applications, RFcircuits and motor control circuitry along with a method of manufacture(including the photolithographic process) therefor, other applicationsand variations of the micromagnetic device and methods of manufacturetherefor are well within the broad scope of the present invention. Itshould also be clear that the precise dimensional and other quantitativeinformation and the specified materials are submitted for illustrativepurposes only.

For a better understanding of integrated circuits and methods ofmanufacture therefor see Handbook of Sputter Deposition Technology, byK. Wasa and S. Hayakawa, Noyes Publications (1992); Thin FilmTechnology, by R. W. Berry, P. M. Hall and M. T. Harris, Van Nostrand(1968); Thin Film Processes, by J. Vossen and W. Kern, Academic (1978);and Handbook of Thin Film Technology, by L. Maissel and R. Glang, McGrawHill (1970). For a general reference regarding electronics includingdata transmission systems see Reference Data for Engineers: Radio,Electronics, Computers and Communications, 7th edition, Howard W. Sams &Company (1988) and power electronics, power magnetic devices and powerconverter topologies see Principles of Power Electronics, by J.Kassakian, M. Schlecht, Addison-Wesley Publishing Company (1991). Theaforementioned references are herein incorporated by reference.

Although the present invention has been described in detail, thoseskilled in the art should understand that they can make various changes,substitutions and alterations herein without departing from the spiritand scope of the invention in its broadest form.

What is claimed is:
 1. An integrated circuit comprising: a substrate; aninsulator located over said substrate; a capacitor located over saidsubstrate; a metallic adhesive located over said insulator; and amicromagnetic device, including; a ferromagnetic core located over saidadhesive, said adhesive forming a bond between said insulator and saidferromagnetic core to secure said ferromagnetic core to said substrate,and at least one winding, located proximate said ferromagnetic core, toimpart a desired magnetic property to said ferromagnetic core, saidmicromagnetic device electrically coupled to said capacitor.
 2. Theintegrated circuit as recited in claim 1 wherein said micromagneticdevice is selected from the group consisting of: an inductor, and atransformer.
 3. The integrated circuit as recited in claim 1 whereinsaid integrated circuit is device selected from the group consisting of:a band pass filter, a low pass filter, a notch filter, and a high passfilter.
 4. The integrated circuit as recited in claim 1 furthercomprising a transistor located over said substrate and electricallycoupled to said micromagnetic device.
 5. The integrated circuit asrecited in claim 4 wherein said integrated circuit is selected from thegroup consisting of: a RF circuit, a motor control circuit, a datatransmission circuit, and a power processing circuit.
 6. The integratedcircuit as recited in claim 4 wherein said transistor is a metal-oxidesemiconductor field-effect transistor (MOSFET).
 7. The integratedcircuit as recited in claim 1 wherein said metallic adhesive comprises aplurality of layers.
 8. The integrated circuit as recited in claim 1wherein said ferromagnetic core contains an alloy material.
 9. Theintegrated circuit as recited in claim 1 wherein said insulator includesan organic polymer.
 10. An integrated circuit, comprising: a substrate;a capacitor located over said substrate, including: a first capacitiveplate layer located over said substrate, a dielectric layer located oversaid first capacitive plate layer, a second capacitive plate layerlocated over said dielectric layer; and a micromagnetic deviceelectrically coupled to said capacitor, including: a first conductivewinding layer located over said substrate proximate said capacitor, afirst insulative layer located over said first conductive winding layer,a metallic adhesive located over said first insulative layer, and aferromagnetic core located over said metallic adhesive, said adhesiveforming a bond between said first insulative layer and saidferromagnetic core to secure said ferromagnetic core to said substrate.11. The integrated circuit as recited in claim 10 further comprising apassivation layer interposed between said substrate and said firstcapacitive plate layer and said first conductive winding layer.
 12. Theintegrated circuit as recited in claim 10 wherein said micromagneticdevice further comprises a second insulative layer located over saidferromagnetic core.
 13. The integrated circuit as recited in claim 12wherein said micromagnetic device further comprises a second conductivewinding layer located over said second insulative layer.
 14. Theintegrated circuit as recited in claim 13 wherein said micromagneticdevice further comprises a third insulative layer located over saidsecond conductive winding layer.
 15. The integrated circuit as recitedin claim 10 wherein said capacitor and said micromagnetic device furthercomprise at least one terminal.
 16. The integrated circuit as recited inclaim 10 wherein said metallic adhesive comprises a layer that containsa material selected from the group consisting of: zirconium; andhafnium.
 17. The integrated circuit as recited in claim 10 wherein saidmetallic adhesive comprises a layer that contains a material selectedfrom the group consisting of: vanadium; niobium; and tantalum.
 18. Theintegrated circuit as recited in claim 10 wherein said metallic adhesivecomprises a layer that contains a material selected from the groupconsisting of: chromium; molybdenum; and tungsten.
 19. The integratedcircuit as recited in claim 10 wherein said metallic adhesive comprisesa layer that contains a material selected from the group consisting of:gold; silver; platinum; palladium; and copper.
 20. The integratedcircuit as recited in claim 10 wherein said ferromagnetic core containsan alloy material.
 21. The integrated circuit as recited in claim 10wherein said first insulative layer includes an organic polymer.
 22. Theintegrated circuit as recited in claim 10 wherein said micromagneticdevice is selected from the group consisting of: an inductor, and atransformer.
 23. The integrated circuit as recited in claim 10 whereinsaid integrated circuit is device selected from the group consisting of:a band pass filter, a low pass filter, a notch filter, and a high passfilter.
 24. The integrated circuit as recited in claim 10 furthercomprising a transistor located over said substrate and electricallycoupled to said micromagnetic device.
 25. The integrated circuit asrecited in claim 24 wherein said integrated circuit is selected from thegroup consisting of: a RF circuit, a motor control circuit, a datatransmission circuit, and a power processing circuit.
 26. The integratedcircuit as recited in claim 24 wherein said transistor is a metal-oxidesemiconductor field-effect transistor (MOSFET).